DC generator

[pablomargareto]

Dear community,

I would need help for a technical question. I want to use a motor for generate electricity. I want to do it within a small wheel (about 8cm diameter) and I want it generates around 2W at 200rpm. Do you know a motor matching this requirements?

I was thinking about this one: [URL unfurl="true"]http://www.rctimer.com/product_914.html[/url]

But I don't know how much power it would generate with so low RPM. It is also importan it does not generate too much noise...

Any idea?

 

[pmrobert]

My suggestion is not a motor but may be an avenue of investigation. I would take a look at the small wind generators commonly found on sailboats.

 

[waross]

Bicycle generator?
A toy permanent magnet motor?
Two watts will be easy if you don't care about the voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[pablomargareto]

Hi Bill,

I think it is an option, but not the most efficient. All that I have seen so far are small motors with a gear box. I need a quiet high torque since it will be running at 200rpm...

I find more interesting approach a wind turbine of 8cm diameter! They are not easy to find at all! Nobody wants wind turbines for generate only 2 Watts!

I think I will do one myself, based on this:
[URL unfurl="true"]http://www.thingiverse.com/thing:55321[/url]

Best regards

 

[waross]

The first motor you link to will generate about 0.37 Volts at 200 RPM. At first approximation that will generate about 3.5 Watts at 9.6 Amps into a suitable load resistance. However at such a low speed the stator resistance will become significant and introduce non-linearity into the simple solution. In real life, expect much less than 3.5 Watts at 200 RPM.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[pablomargareto]

Hi waross,

I was thinking in do it myself, similar to the one in the link. I want to do an axial generator with dual rotor. Then I can increase significantly the amperage. I need to find the proper magnets to generate 2W at 200rpm.

As you said, the stator will increase the resistance. But I don't get the part of non-linearity? What does it mean?

 

[waross]

Often the armature resistance may be neglected for estimating the effect of small speed changes on the voltage of a motor. As the speed and the voltage drop, the armature resistance becomes more significant. At rated speed, the armature resistance may be negligible relative to the load resistance. At 200 RPM, the armature resistance may exceed the load resistance and the motor losses may become greater than the energy delivered to the load.
As the voltage is lowered, the load resistance must also be lowered to maintain the same current.

Bill
--------------------
"Why not the best?"
Jimmy Carter